The studies proposed here will investigate the molecular mechanisms of pheromone detection and sensory transduction in the vomeronasal organ (VNO). Our laboratory has been instrumental in identifying key components of the vomeronasal signaling apparatus, including the TRP2 ion channel, two distinct families of putative pheromone receptors the V1Rs and V2Rs, and the major histocompatibility complex (MHC) class 1b molecule (M10) and the accessory molecule b2-microglobulin (beta2m) that form a functional receptor complex with V2Rs. In order to further understand the process of signal detection in the VNO, it is critical to determine the respective roles of the V1R and V2R receptor families in vomeronasal function and to analyze the functional and molecular characteristic of each type of receptor activation. The objective of this research is to use molecular, genetic and physiological approaches to investigate the characteristics of V1R and V2R function. A major impediment in chemosensory research has been the difficulty in studying olfactory and vomeronasal receptor function in vitro by lack of proper surface expression in heterologous cells. We developed a cloning strategy based on differential screening of cDNA libraries constructed from individual VNO neurons, which led to the isolation of V2R molecular escorts, the non classical class 1b molecules M10s and M1s. The first aim of this proposal is to use the same strategy combined to genomic and biochemical approaches to identify and characterize molecules involved in V1R function within apical VNO neurons. In the second aim we will pursue the biochemical and genetic analysis of the class lb molecules M10s in order to determine the mechanism by which they enhance surface expression of V2R and participate directly or indirectly to the recognition of chemosensory cues. Finally, in the third aim, we will generate mouse mutant lines in order to directly investigate the activation of V1Rs and V2Rs in vivo and gain insight into signal detection and sensory transduction by the various types of VNO receptor neurons.